Metals News

The imminent release of ISO 6892-1:2016 will provide further clarification on the significant changes that were introduced in ISO 6892-1:2009. In 2009, ISO 6892-1 replaced and combined both the previous ISO 6892 and the widely used EN 10002-1:2001 standards. It incorporated many changes, but most notably, it introduced the testing rates based on strain rate (Method A).

Method A was the recommended approach and was based on maintaining a strain rate. The traditional test method from EN 10002:2001, based on maintaining a stress rate during the elastic region, became Method B. The introduction of Method A caused confusion. Many understood this as only being achievable using equipment capable of closed-loop strain control, but this is not true. It is possible to conform to Method A using a constant crosshead speed. To better clarify the requirements of Method A, ISO 6892-1:2016 now includes two clearly defined approaches, Method A1 (Closed-Loop Strain Control) and Method A2 (Constant Crosshead Separation Rate).

Implementing strain control as per ISO 6892-1, coupled with utilizing automatic specimen measurement, hydraulic DuraSync grips, or an Automatic Axial and Transverse Extensometer can make a dramatic difference in the total test time when compared with a traditional setup. In the below video, there is a 36% reduction in total cycle time by making slight adjustments to the testing system.

There are many challenges in the QC world: Variability of test results, repetitive tasks/better use of skilled labor, throughput, and safety and ergonomics.

To set the stage, let’s look at a typical test cycle in detail. An operator:

Step 1: Enters the batch or specimen ID into the testing software

Step 2: Measures the specimen’s width and thickness (often in 3 locations, then the average is taken)

Step 3: Enters the data into the testing software

Step 4: Loads the specimen into the grips

Step 5: Attaches the extensometer

Step 6: Starts the test

After performing these 6 steps, the operator must then stand at the system and wait for the test to end, which could take anywhere from 30 seconds to 20 mins, depending on the material. Once complete, the operator must remove the specimen from the testing machine and often needs to transfer the results to a LIMS or network database for analysis.

These steps take up valuable operator time and have the potential for introducing variability. When analyzing common sources of variability, operator influence can have an effect on the total measurement error. Procedural errors, technique, system set up, and specimen handling all come into play and can change drastically between different operators.

An easy way to address many of these issues is to add some level of automation. What many labs may not be aware of is there are many incremental levels of automation tools and devices that can aide in removing operator variability. The range of automation includes a simple barcode reader to instantly enter ID’s into the testing software, or an automatic specimen measurement device to efficiently measure specimens, or a full robotic automation system with one robot feeding two tensile frames.

Automation can solve the four typical pain points in QC by decreasing the variability of results, allowing skilled labor to perform other tasks, improving throughput, and creating a safer, more ergonomic environment for operators.

User groups provide a forum to discuss and promote best practices and to generate cross-fertilization of ideas. Our latest workshop, which focused on Very High Speed (VHS) materials testing in Beijing, was attended by nearly 30 representatives conducting experiments on strain rate testing for academic research, for engineering efforts within individual companies, and to supply and exchange high-value engineering data between organizations.

Workshop Highlights

Guest speaker David Williams, WMG at the University of Warwick, provided insight into how one of our earlier VHS systems has found increasingly varied applications and come to form an essential part of their USP in bridging the gap between research and industry

Thought-provoking presentation by LaVision GmbH on how digital image correlation can be used for research into mechanical tests at high speed

With the success of this meeting and the growing urgency for consistent data to support lightweight automotive design and development worldwide, we hope that this could form the foundation of an international series of meetings.